In 2005, an estimated 1.6 million persons living in the United States had a limb amputation, with an expected increase in this population reaching 2.2 million by 2020. (Ziegler-Graham, K., MacKenzie, E. J., Ephraim, P. L., Travison, T. G. & Brookmeyer, R. Estimating the prevalence of limb loss in the United States: 2005 to 2050. Arch. Phys. Med. Rehabil. 89, 422-429 (2008)) Data reported by the Joint Theater Trauma Registry and Military Amputee Research Program showed that between October 2001 and June 2006, 423 service members suffered one or more major limb amputation. (Ziegler-Graham, K., et al., Estimating the prevalence of limb loss in the United States: 2005 to 2050. Archives of physical medicine and rehabilitation, 2008. 89(3): p. 422-429) In 2010 it was reported that 950 soldiers sustained combat-related amputations and in 2012 it had risen to 1599 from all recent conflicts. (Stinner, D. J., et al., Prevalence of Late Amputations During the Current Conflicts in Afghanistan and Iraq. Military Medicine, 2010. 175(12): p. 1027-1029; Fischer, H. U.S. Military Casualty Statistics: Operation New Dawn, Operation Iraqi Freedom, and Operation Enduring Freedom. (2012)).
The prosthetic socket is intended to capture and transfer movements of the residual limb (RL) to the prosthesis. This is challenging, especially for RLs with a high soft tissue to bone ratio. Soft tissues are not suited to be mechanical load bearers, and excessive forces and motions can have damaging effects and diminish the efficacy of the prosthesis. (Dudek N L, Marks M B, Marshall S C and Chardon J P. Dermatologic conditions associated with use of a lower-extremity prosthesis. Archives of physical medicine and rehabilitation. 2005; 86: 659-63; Highsmith M J, Highsmith J T and Kahle J T. Identifying and Managing Skin Issues With Lower-Limb Prosthetic Use. inMotion January/February. 2011; 21: 41-3) The socket serves as the interface between the human and prosthesis and is important in the comfort and acceptance of the prosthesis. Previous studies have found motion occurs at the interface of both models and a practical setting (Wernke, BMES Conference 2011, Poster; Highsmith, J P O July 2007, Vol. 19, Issue 3, 84-90). A survey of prosthesis users found that socket interface comfort was rated the most important factor and 18.4% report being fit with a new prosthesis at least once a year. (Schultz A E, Baade S P and Kuiken T A. Expert opinions on success factors for upper-limb prostheses. Journal of Rehabilitation Research and Development. 2007; 44: 483; Pezzin L E, Dillingham T R, MacKenzie E J, Ephraim P and Rossbach P. Use and satisfaction with prosthetic limb devices and related services. Archives of physical medicine and rehabilitation. 2004; 85: 723-9)
Some military service members place particularly high demands on their prosthesis and many are dissatisfied with the current technology. In fact, after noticing a ceiling effect on the amputee mobility predictor, the Comprehensive High Level Activity Mobility Predictor (CHAMP) was developed. (Gaunaurd, I. The Comprehensive High-level Activity Mobility Predictor (CHAMP): A Performance-based Assessment Instrument to Quantify High-level Mobility in Service Members with Traumatic Lower Limb Loss. Open Access Diss. (2012)). Further, the complexity of recent military amputees is greater than in the past. Gailey found an increased incidence of other combat associated injuries and more surgeries after limb loss (Gailey, R. et al. Unilateral lower-limb loss: Prosthetic device use and functional outcomes in service members from Vietnam War and OIF/OEF conflicts. J. Rehabil. Res. Dev. 47, 317 (2010)).
Limb movement within a prosthesis has been measured in the laboratory, but a practical method for monitoring limb movement is not currently available. Similarly, no efficient method to measure socket slip has been developed which can aid in comparing different models to each other or aid in the fitting process. Thus far, prosthetic socket designs have failed to successfully incorporate active elements.
Socket movement has long been understood as very important to prosthetic fit, but has been difficult to measure. Studies have investigated the movement occurring at the socket interface to better understand socket fit and design. Appoldt rigidly attached a pen to the socket and analyzed the ink trail left on the limb to measure slip, but data had to be analyzed post testing and limited accuracy. (Appoldt F A, Bennett L and Contini R. The results of slip measurements in above-knee suction sockets. Bull Prosthet Res Fall. 1968: 106-12)
As methods have improved, more movement has been detected. A variety of radiologic methods have been used including X-ray, fluoroscopy, and Dynamic Roentgen Stereo Photogrammetric Analyses (DRSA) scanning. These methods are limited in their field of view, expose the subject to ionizing radiation and are not practical for use outside of the clinic. For example, Commean measured slip using x-ray by placing lead markers on the skin surface and inner wall of the socket, but was limited to static poses. (Commean P K, Smith K E and Vannier M W. Lower extremity residual limb slippage within the prosthesis. Archives of physical medicine and rehabilitation. 1997; 78: 476-85) Motion from roentgengraphic applications showed bone movement relative to the socket between 22 mm and 36 mm. (Lilja, M., Johansoon, T. & Oberg, T. Movement of the tibial end in a PTB prosthesis socket: a sagittal X-Ray study of the PTB prosthesis. Prosthet. Orthot. Int. 17, 21-26 (1993); Narita, H., Yokogushi, K., Shii, S., Kakizawa, M. & Nosaka, T. Suspension effect and dynamic evaluation of the total surface bearing (TSB) trans-tibial prosthesis: a comparison with the patellar tendon bearing (PTB) trans-tibial prosthesis. Prosthet. Orthot. Int. 21, 175-178 (1997)). Computed tomography was used and found movement of 10 mm under static loading conditions. (Commean, P. K., Brunsden, B. S., Smith, K. E. & Vannier, M. W. Below-knee residual limb shape change measurement and visualization. Arch. Phys. Med. Rehabil. 79, 772-782 (1998)). DRSA used during stepping tasks showed up to a 16 mm translation of the socket, however the DRSA viewing window is not large enough to accommodate walking. (Papaioannou, G., Mitrogiannis, C., Nianios, G. & Fiedler, G. Assessment of Internal and External Prosthesis Kinematics during Strenuous Activities Using Dynamic Roentgen Stereophotogrammetric Analysis. J. Prosthetics Orthot. 22, 91-105 (2010)). As illustrated above, motion analysis is time consuming and movement can still be difficult to access. (Gholizadeh, H. et al. Transtibial prosthetic socket pistoning: Static evaluation of Seal-In® X5 and Dermo® Liner using motion analysis system. Clin. Biomech. Bristol Avon (2011); Highsmith, M. J., Carey, S. L., Koelsch, K. W., Lusk, C. P. & Maitland, M. E. Kinematic Evaluation of Terminal Devices for Kayaking With Upper Extremity Amputation. J. Prosthetics Orthot. 19, 84-90 (2007)).
The bone position relative to the socket has also been measured using radiological, acoustic, optical, and marker-based motion analysis techniques to quantify socket movement. (Söderberg B, Ryd L and Persson B M. Roentgen stereophotogrammetric analysis of motion between the bone and the socket in a transtibial amputation prosthesis: a case study. JPO: Journal of Prosthetics and Orthotics. 2003; 15: 95; Grevsten S and Erikson U. A roentgenological study of the stump-socket contact and skeletal displacement in the PTB-Suction Prosthesis. Upsala Journal of Medical Sciences. 1975, 80: 49-57; Kahle J T. A case study using fluoroscope to determine the vital elements of transfemoral interface design. JPO: Journal of Prosthetics and Orthotics. 2002; 14: 121; Lilja M, Johansson T and Öberg T. Movement of the tibial end in a PTB prosthesis socket: a sagittal X-ray study of the PTB prosthesis. Prosthetics and Orthotics International. 1993; 17: 21-6; Papaioannou G, Mitrogiannis C, Nianios G and Fiedler G. Assessment of amputee socket-stump-residual bone kinematics during strenuous activities using Dynamic Roentgen Stereogrammetric Analysis. Journal of biomechanics. 2010; 43: 871-8; Convery P and Murray K. Ultrasound study of the motion of the residual femur within a trans-femoral socket during gait. Prosthetics and Orthotics International. 2000; 24: 226-32; Sanders J E, Karchin A, Fergason J R and Sorenson E A. A noncontact sensor for measurement of distal residual-limb position during walking. Journal of Rehabilitation Research and Development. 2006; 43: 509; Gholizadeh H, Osman N, Kamyab M, Eshraghi A, Abas W and Azam M. Transtibial prosthetic socket pistoning: Static evaluation of Seal-In® X5 and Dermo® Liner using motion analysis system. Clinical Biomechanics. 2011; Freilich R. Biomechanical model of transhumeral prostheses. University of South Florida. 2009, Masters Thesis) However, radiological methods limited participants to static positions, acoustic methods required bulky hardware added to the socket, embedded optical sensors have only been used to measure pistoning other aspects of socket movement, and marker-based motion analysis have not determined the position of tissues within the socket. Additionally, these methods could not detect slip occurring between the socket and skin surface.
Sanders developed an optical range sensor to measure the amount of pistoning occurring in lower limb prostheses. (Sanders, J. E., et al., A noncontact sensor for measurement of distal residual-limb position during walking. Journal of Rehabilitation Research and Development, 2006. 43(4): p. 509) The study found an average of 41.7 mm of movement during gait but it could not distinguish between slip and soft tissue deformation. (Sanders, J. E., et al., A noncontact sensor for measurement of distal residual-limb position during walking. Journal of Rehabilitation Research and Development, 2006. 43(4): p. 509). A photographic method was used for clinical purposes under several static loading conditions with an average translation of the socket/residual limb in the vertical direction shown to be 9 mm. (Gholizadeh, H. et al. A new approach for the pistoning measurement in transtibial prosthesis. Prosthet. Orthot. Int. (2011)).
Through various measurements, static loading/unloading produces between 10 mm movement and dynamic loading/unloading during gait more than double that amount of movement. All of these studies were on small sample sizes. None of these existing methods allow for a simple nonintrusive method of measuring socket movement during the course of normal activities.
One explanation for the dissatisfaction with current socket designs is the inability of the socket to adjust to changes in RL volume which can result in poor socket fit. Adjustable interfaces have been developed to address changes in RL volume. In these adjustable interfaces, the user can change the internal conditions to account for changes in the residual limb. The residual limb volume can fluctuate over short time periods throughout the day in response to biological and environmental factors; therefore sockets that maintain one shape or one vacuum pressure may not provide adequate suspension over the course of wearing the prosthesis.
A variety of options exist for the method of suspension of a prosthetic socket. Suspension options include self-suspending, harness, pin locking, or vacuum/suction suspended prostheses. One of the newest sockets offering self-suspension is the High-Fidelity socket designed by Randall Alley. (Alley, R., Biomechanical Discussion of Current and Emergent Upper-Limb Prosthetic Interface Designs. The Academy Today, 2009. 5(3); Alley, R. The High-Fidelity Interface: Skeletal Stabilization through Alternating Soft Tissue Compression and Release. 2011. Myoelectric Symposium) The socket design features four longitudinal struts that provide a high degree of soft tissue compression, taking hold of the underlying bone more so than traditional sockets. Concurrent with the longitudinal struts are four windows that provide soft tissue relief. The Highfidelity socket design is believed to have better contact with the long bones of the residual limb and limit motion between the user and prosthesis. (Discussion of Current and Emergent Upper-Limb Prosthetic Interface Designs. The Academy Today, 2009. 5(3))
The RevoLimb (Technology B. RevoFit: Control Your Comfort. [Cited July 2013]) is another self-suspending socket which incorporates movable panels that can be adjusted by the user via a dial to create a tighter or looser fit thus adjusting socket volume. The RevoLimb is based on the same technology used in the Boa closure system (Boa Technology, Steamboat Springs, Colo.).
With regard to vacuum systems, the SmartPuck (5280 Prosthetics. Introducing SmartPuck. [cited July 2013]) and LimbLogic (WillowWood. The Evolution of LimbLogic Provides Elevated Vacuum in an Easier to Use System. [cited July 2013]) are adjustable vacuum systems that are sealed into the socket. Users of these systems can adjust the vacuum settings inside the socket using an Apple iTouch or Bluetooth fob respectively.
While each of the above systems is adjustable, they each require manual adjustment by the user, since what constitutes a good socket fit is still being investigated. These systems do not represent an actively changing system. Vacuum assisted sockets have been shown to reduce volume fluctuations, but many people with an amputation do not prefer vacuum assisted sockets because of comfort, ease of use, and reduced steps taken. (Sanders, J. E. and S. Fatone, Residual limb volume change: Systematic review of measurement and management. J Rehabil Res Dev, 2011. 48(8): p. 949-86; Klute, G. K. et al. Vacuum-assisted socket suspension compared with pin suspension for lower extremity amputees: effect on fit, activity, and limb volume. Arch. Phys. Med. Rehabil. 92, 1570-1575 (2011)). While these systems allow for the adjustment of socket fit, the timing and amount of adjustment are controlled by the user. The user may not be able accurately detect and resolve issues with socket fit. For instance, excessive slippage of the socket should be avoided; however, absence of slippage may result in other problems. A study investigating the effects of friction and shear using pig skin found an inverse correlation between the magnitude of shear force and the time until skin breakdown occurred. (Goldstein, B. and J. Sanders, Skin response to repetitive mechanical stress: a new experimental model in pig. Archives of physical medicine and rehabilitation, 1998. 79(3): p. 265-272)
The inventors previously studied a pneumatic adjustable socket system designed for upper extremities, herein incorporated in its entirety by reference. [VA RR&D#A9226-R Take home study of an advanced upper limb prosthesis, PI: Resnik] This system reacted to changes in pressure within the pneumatic system to adjust level of air pressure in pneumatic bladders, which subsequently adjusted socket volume. The inventors discovered that changes in pressure could be the result of many things. The inventors also found that it was difficult to discriminate between movement, which they wanted to compensate for, and muscle contraction, which they did not want to compensate for. These results led the inventors to ascertain that a measure of the limb itself was required to provide adequate feedback to a dynamic adjustable socket system.
In order to alleviate the disadvantages of the prior art, the inventors have developed a dynamic socket system which utilizes one or more Slip Detection Sensors (SDS) to provide feedback to improve the comfort and improve adjustments to short and long-term changes of the residual limb as well as a method to capture socket movements using motion analysis to accommodate limited space between the socket trim-lines and the body and approximate residual limb bone position within the socket. (Freilich R. Biomechanical model of transhumeral prostheses. University of South Florida. 2009, Masters Thesis).
The Slip Detection Sensor can directly measure slip between the residual limb and prosthetic socket or orthosis to provide dynamic feedback to adjust the prosthetic socket. The socket system enhances long-term socket performance and fit of prostheses through the development of a flexible socket that uses a novel Slip Detection Sensor, the interface of which is able to detect motions that can damage the soft tissues and adjust the socket or warn the prosthesis user before the injuries occur. While this project is targeted to military service members with amputations it will also benefit veterans and civilians with amputations.